@article{MenzelHeuerPuhlmannetal.2013,
  author    = {Menzel, Ralf and Heuer, Axel and Puhlmann, Dirk and Dechoum, K. and Hillery, M. and Spaehn, M. J. A. and Schleich, W. P.},
  title     = {A two-photon double-slit experiment},
  series = {Journal of modern optics},
  volume    = {60},
  journal   = {Journal of modern optics},
  number    = {1},
  publisher = {Routledge, Taylor \& Francis Group},
  address   = {Abingdon},
  issn      = {0950-0340},
  doi       = {10.1080/09500340.2012.746400},
  pages     = {86 -- 94},
  year      = {2013},
  abstract  = {We employ a photon pair created by spontaneous parametric down conversion (SPDC) where the pump laser is in the TEM01 mode to perform a Young's double-slit experiment. The signal photon illuminates the two slits and displays interference fringes in the far-field while the idler photon measured in the near-field in coincidence with the signal photon provides us with which-slit' information. We explain the results of these experiments with the help of an analytical expression for the second-order correlation function derived from an elementary model of SPDC. Our experiment emphasizes the crucial role of the mode function in the quantum theory of radiation.},
  language  = {en}
}
@article{MenzelHeuerMilonni2019,
  author    = {Menzel, Ralf and Heuer, Axel and Milonni, Peter W.},
  title     = {Entanglement, Complementarity, and Vacuum Fields in Spontaneous Parametric Down-Conversion},
  series = {Atoms},
  volume    = {7},
  journal   = {Atoms},
  number    = {1},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {2218-2004},
  doi       = {10.3390/atoms7010027},
  pages     = {14},
  year      = {2019},
  abstract  = {Using two crystals for spontaneous parametric down-conversion in a parallel setup, we observe two-photon interference with high visibility. The high visibility is consistent with complementarity and the absence of which-path information. The observations are explained as the effects of entanglement or equivalently in terms of interfering probability amplitudes and also by the calculation of a second-order field correlation function in the Heisenberg picture. The latter approach brings out explicitly the role of the vacuum fields in the down-conversion at the crystals and in the photon coincidence counting. For comparison, we show that the Hong-Ou-Mandel dip can be explained by the same approach in which the role of the vacuum signal and idler fields, as opposed to entanglement involving vacuum states, is emphasized. We discuss the fundamental limitations of a theory in which these vacuum fields are treated as classical, stochastic fields.},
  language  = {en}
}